[tip:perfcounters/urgent] perf_counter: Fix /0 bug in swcounters
From: tip-bot for Peter Zijlstra
Date: Sat Aug 29 2009 - 07:26:11 EST
Commit-ID: eced1dfcfcf6b0a35e925d73916a9d8e36ab5457
Gitweb: http://git.kernel.org/tip/eced1dfcfcf6b0a35e925d73916a9d8e36ab5457
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Fri, 28 Aug 2009 17:10:47 +0200
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Sat, 29 Aug 2009 13:20:11 +0200
perf_counter: Fix /0 bug in swcounters
We have a race in the swcounter stuff where we can start
counting a counter that has never been enabled, this leads to a
/0 situation.
The below avoids the /0 but doesn't close the race, this would
need a new counter state.
The race is due to perf_swcounter_is_counting() which cannot
discern between disabled due to scheduled out, and disabled for
any other reason.
Such a crash has been seen by Ingo:
[ 967.092372] divide error: 0000 [#1] SMP
[ 967.096499] last sysfs file: /sys/devices/system/cpu/cpu15/cache/index2/shared_cpu_map
[ 967.104846] CPU 5
[ 967.106965] Modules linked in:
[ 967.110169] Pid: 3351, comm: hackbench Not tainted 2.6.31-rc8-tip-01158-gd940a54-dirty #1568 X8DTN
[ 967.119456] RIP: 0010:[<ffffffff810c0aba>] [<ffffffff810c0aba>] perf_swcounter_ctx_event+0x127/0x1af
[ 967.129137] RSP: 0018:ffff8801a95abd70 EFLAGS: 00010046
[ 967.134699] RAX: 0000000000000002 RBX: ffff8801bd645c00 RCX: 0000000000000002
[ 967.142162] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8801bd645d40
[ 967.149584] RBP: ffff8801a95abdb0 R08: 0000000000000001 R09: ffff8801a95abe00
[ 967.157042] R10: 0000000000000037 R11: ffff8801aa1245f8 R12: ffff8801a95abe00
[ 967.164481] R13: ffff8801a95abe00 R14: ffff8801aa1c0e78 R15: 0000000000000001
[ 967.171953] FS: 0000000000000000(0000) GS:ffffc90000a00000(0063) knlGS:00000000f7f486c0
[ 967.180406] CS: 0010 DS: 002b ES: 002b CR0: 000000008005003b
[ 967.186374] CR2: 000000004822c0ac CR3: 00000001b19a2000 CR4: 00000000000006e0
[ 967.193770] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 967.201224] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 967.208692] Process hackbench (pid: 3351, threadinfo ffff8801a95aa000, task ffff8801a96b0000)
[ 967.217607] Stack:
[ 967.219711] 0000000000000000 0000000000000037 0000000200000001 ffffc90000a1107c
[ 967.227296] <0> ffff8801a95abe00 0000000000000001 0000000000000001 0000000000000037
[ 967.235333] <0> ffff8801a95abdf0 ffffffff810c0c20 0000000200a14f30 ffff8801a95abe40
[ 967.243532] Call Trace:
[ 967.246103] [<ffffffff810c0c20>] do_perf_swcounter_event+0xde/0xec
[ 967.252635] [<ffffffff810c0ca7>] perf_tpcounter_event+0x79/0x7b
[ 967.258957] [<ffffffff81037f73>] ftrace_profile_sched_switch+0xc0/0xcb
[ 967.265791] [<ffffffff8155f22d>] schedule+0x429/0x4c4
[ 967.271156] [<ffffffff8100c01e>] int_careful+0xd/0x14
Reported-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
LKML-Reference: <1251472247.17617.74.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
kernel/perf_counter.c | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 7d4bb83..d7cbc57 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -4066,6 +4066,7 @@ perf_counter_alloc(struct perf_counter_attr *attr,
hwc->sample_period = attr->sample_period;
if (attr->freq && attr->sample_freq)
hwc->sample_period = 1;
+ hwc->last_period = hwc->sample_period;
atomic64_set(&hwc->period_left, hwc->sample_period);
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/